I was at an event recently where someone had one of these, and it drew blood. This has been mentioned in the reviews, but that's my only personal experience, since I don't own one (yet).

I usually waterproof all my leather items, and if we have something that comes into contact with body fluids (which this will, since it can break the skin) it's not shared with other partners. So, once I have one of these it'll be for me only.